Scorch retarding crosslinking compositions comprising a hydroquinone, a sulfur accelerator, a coagent and a free radical initiator

ABSTRACT

A crosslinkable composition of a polymeric thermoplastic and/or elastomeric material which is susceptible to scorching when processed at elevated temperatures, prior to crosslinking, in the presence of a free radical initiator, is protected against such scorching by the incorporation therein of a mixture of at least one hydroquinone compound and a sulfur accelerator. This mixture may also contain at least one monomeric allylic, methacrylic, acrylic or diene type coagent. The mixture exhibits a synergistic effect resulting in improved scorch protection for peroxide cured systems when compared with the protection afforded by the components singly.

This is a continuation of application Ser. No. 08/228,821 filed Apr. 18,1994, now abandoned, which is a continuation of application Ser. No.07/673,881 filed Mar. 22, 1991, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to the prevention of scorching prior tocrosslinking of a peroxide or azo compound crosslinkable thermoplasticand/or elastomeric composition.

A major difficulty in using organic peroxides or azo compounds incrosslinking (curing) elastomeric and thermoplastic materialsapplications is that they may initiate premature crosslinking (i.e.scorch) during compounding and/or processing prior to the actual phasein the overall process when curing is desired. With conventional methodsof compounding, such as milling, Banbury, or extrusion, scorch occurswhen the time-temperature relationship results in a condition where theperoxide or azo initiator undergoes thermal decomposition, initiatingthe crosslinking reaction whereby gel particles in the mass of thecompounded polymer may be formed. The presence of these gel particlesleads to inhomogeneity of the final product. Excessive scorch reducesthe plastic properties of the material so that it can no longer beprocessed, resulting in the loss of the entire batch.

Therefore, it has been widely accepted that the peroxide of choice musthave a high enough activation temperature so that compounding and/orother processing steps can be successfully completed prior to the finalcuring step. Thus one method of avoiding scorch is to use an initiatorthat is characterized by having a high 10 hour half-life temperature.The disadvantage to this approach is that one subsequently obtains alonger cure time, which results in lower throughput. High curetemperatures can be used but this runs into the disadvantage of higherenergy costs.

A further way of avoiding scorch is to lower the compounding and/orprocessing temperature to improve the scorch safety margin of thecrosslinking agent. This option however may be somewhat limited in scopedepending upon the polymer and/or process involved. In addition, curingat the lower temperature requires longer cure times and results in lowerthroughput. Prior to the present invention, certain additives wereincorporated into compositions which reduced the tendency for scorching.For example, British patent 1,535,039 discloses the use of organichydroperoxides as scorch inhibitors for peroxide-cured ethylene polymercompositions. U.S. Pat. No. 3,751,378 discloses the use of N-nitrosodiphenylamine or N,N'-dinitroso-para-phenylamine as retardersincorporated in a polyfunctional acrylate crosslinking monomer forproviding long Mooney scorch times in various elastomer formulations.U.S. Pat. No. 3,202,648 discloses the use of nitrites such asisoamylnitrite, tert-decyl nitrite and others as scorch inhibitors forpolyethylene. U.S. Pat. No. 3,954,907 discloses the use of monomericvinyl compounds as protection against scorch. U.S. Pat. No. 3,335,124describes the use of aromatic amines, phenolic compounds,mercaptothiazole compounds, bis(N,N-disubstituted thiocarbonyl)sulfides,hydroquinones and dialkyldithiocarbamate compounds. The use of mixturesof the active compounds in preventing scorch is neither taught norsuggested. U.S. Pat. No. 4,632,950 discloses the use of mixtures of twometal salts of disubstituted dithiocarbamic acid, wherein one metal saltis based on copper. This reference does not teach the use of suchmixtures with neat peroxides. For some applications, it is desirable ormandatory to use liquid or neat peroxides, as described in this currentinvention. One such application is in extruded compounding. A commoncommercial process technique employs a liquid peroxide which is sprayedonto polymer pellets or granules to coat them prior to extrusioncompounding. This can provide increased production efficiency andeliminates physical handling of hazardous compounds. This referencepatent teaches that at least one filler must be present. The scorchresistant systems described in this reference are not effective inpolyolefins specifically LDPE, LLDPE, or HDPE. The present invention iseffective in polyolefin systems. Moreover, this reference does not teachthe use of mixtures of hydroquinones and metal salts of disubstituteddithiocarbamic acid.

When employing these prior art methods for extending scorch time, thecure time and/or final crosslink density of the cured composition can beadversely affected, leading to a decrease in productivity and/or productperformance. The present invention overcomes the disadvantages of theprior art in that an improvement in scorch at compounding temperaturesis achieved without significant impact on the final cure time orcrosslink density. This is achieved by incorporation of the cureretarding composition at low additive levels, thereby limiting theeffect on properties. In addition, significant scorch protection isachieved, since the use of the combination of the hydroquinones and asulfur accelerator of the dithiocarbamate or thiuram class results in asynergistic effect on scorch time at the low additive levels employed.

SUMMARY OF THE INVENTION

The present invention provides in a first composition aspect a scorchretarding composition comprising a hydroquinone and at least one sulfuraccelerator.

The tangible embodiments of this composition aspect of the inventionpossess the inherent applied use characteristics of being scorchretarders showing greater effect than equivalent amounts of eithercomponent used separately when incorporated into polymeric compositionswhich are crosslinkable by free radical initiation while notsubstantially affecting final cure time or properties.

Special mention is made of compositions of the first composition aspectof the invention which additionally comprise a coagent.

The invention also provides in a second composition aspect a scorchretarding, curing/crosslinking composition comprising a free radicalinitiator selected from the group consisting of organic peroxides, azocompounds and mixtures thereof, and the scorch retarding composition ofthe first composition aspect of the invention.

The tangible embodiments of this second composition aspect of theinvention possess the inherent applied use characteristics, when blendedinto conventional thermoplastic and/or elastomeric polymers as acrosslinking agent, of providing improved scorch protection for theblended system while not substantially affecting final cure times orcharacteristics.

This invention also provides in a third composition aspect acrosslinkable composition comprising a peroxide or azo compoundcrosslinkable thermoplastic and/or elastomeric polymer, and a scorchretarding curing/crosslinking composition as defined in the secondcomposition aspect of the inventions.

The invention also provides in an improved process for the preparationof a crosslinkable composition comprising a peroxide or azo compoundcrosslinkable thermoplastic and/or elastomeric polymer and a freeradical initiator selected from the group of organic peroxides, azocompounds and mixtures thereof wherein said polymer is compounded withsaid free radical initiator, the improvement comprising performing saidcompounding in the presence of a scorch retarding composition of thefirst composition aspect of the invention.

Special mention is made of processes of this process aspect of theinvention wherein the scorch retarding composition additionallycomprises a coagent.

In the practice of this invention, the preferred blends of hydroquinonesand sulfur accelerators exhibit acceptable solubility in the freeradical initiators when the selected free radical initiator is a liquidor low melting solid. Thus, this new technology will allow for apumpable or a meterable homogeneous crosslinking system that providesease of handling and greater worker safety as well as longer compoundingtimes for better mixing due to the improved scorch protection provided.

Where homogenous liquid or low melting solid crosslinking compositionsare not normally used such as in rubber compounding, and the selectedscorch retarding crosslinking composition is liquid, the hydroquinone,peroxide, sulfur accelerator and optional coagent(s) either asindividual portions, or the entire combined scorch retardingcrosslinking composition may be dispersed on an inert filler (preferablyan inorganic filler) for ease of addition during compounding such as ona rubber mill. A masterbatch on a polymeric binder may be used in thesame fashion for the same purpose.

DETAILED DESCRIPTION

The superior scorch resistance for peroxide and azo crosslinkableelastomeric and/or thermoplastic polymeric systems may be obtained byadmixing, conveniently by employing conventional compounding means, withthe thermoplastic and/or elastomeric polymer which is desired to becrosslinked, a scorch retarding crosslinking composition comprising afree radical initiator selected from the group consisting of organicperoxides, azo compounds and mixtures thereof, a hydroquinone compound,at least one sulfur accelerator, and optionally any of the knownacrylic, methacrylic or allylic monomers.

The scorch retarding curing/crosslinking composition may preferably beblended into the desired polymer as a preformed mixture or theindividual ingredients thereof may be incorporated into the polymerseparately or even as subcombinations of one or more but not all theingredients. If incorporation as individual or subcombinations ofingredients is desired, it is preferred that the hydroquinone, monomers,and/or the sulfur accelerator be blended into the polymer prior toblending of the free radical initiator.

Free Radical Initiators

In accordance with the present invention, compounds well known in theart such as azo initiators and/or organic peroxides (with the exceptionof hydroperoxides and peroxydicarbonates) which upon thermaldecomposition generate free radicals that facilitate thecuring/crosslinking reaction may be employed. Of the free radicalinitiators used as crosslinking agents, the dialkyl peroxides anddiperoxyketal initiators are preferred. A detailed description of thesecompounds may be found in the Encyclopedia of Chemical Technology, 3rdedition, Vol. 17, pp 27-90. (1982)

In the group of dialkyl peroxides, the preferred initiators are:

dicumyl peroxide

di-t-butyl peroxide

t-butyl cumyl peroxide

2,5-dimethyl-2,5-di(t-butylperoxy)-hexane

2,5-dimethyl-2,5-di(t-amylperoxy)-hexane

2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3

2,5-dimethyl-2,5-di(t-amylperoxy)hexyne-3

alpha,alpha-di (t-butylperoxy)-isopropyl!-benzene

di-t-amyl peroxide

1,3,5-tri- (t-butylperoxy)-isopropyl!benzene

1,3-dimethyl-3-(t-butylperoxy)butanol

1,3-dimethyl-3-(t-amylperoxy) butanol

and mixtures thereof.

In the group of diperoxyketal initiators, the preferred initiators are:

1,1-di(t-butylperoxy)-3,3,5-trimethylcyclohexane

1,1-di(t-butylperoxy)cyclohexane

n-butyl 4,4-di(t-amylperoxy)valerate

ethyl 3,3-di(t-butylperoxy)butyrate

2,2-di(t-amylperoxy)propane

3,6,6,9,9-pentamethyl-3-ethoxycarbonylmethyl-1,2,4,5-tetraoxacyclononane;

n-butyl-4,4-bis(t-butylperoxy)-valerate;

ethyl-3,3-di(t-amylperoxy)-butyrate

and mixtures thereof.

Other peroxide, e.g., 00-t-butyl-0-hydrogen monoperoxysuccinate;00-t-amyl-0-hydrogen-monoperoxysuccinate and/or azo initiators e.g.,2,2'-azobis-(2-acetoxypropane) may also be used to provide a crosslinkedpolymer matrix. Mixtures of two or more free radical initiators may alsobe used together as the initiator within the scope of this invention.

Other suitable azo compounds include those described in U.S. Pat. Nos.3,862,107 and 4,129,531 which are incorporated herein by reference.

The amount of the scorch retarding crosslinking composition aspect ofthis invention to be incorporated in a crosslinkable composition willreadily be selected by one of skill in the art to be sufficient toafford the desired degree of crosslinking. When the free radicalinitiator component is an organic peroxide, the scorch retardingcrosslinking composition may be employed in quantities to provide aconcentration of peroxide in the crosslinkable composition ranging from0.01 to 30 parts by weight, preferably, from 0.01 to 20 parts by weight,most preferably from 0.5 to 4.0 parts by weight for each 100 parts byweight of polymer.

Sulfur Accelerators

Any of the known sulfur accelerators as understood by one of skill inthe art to be employed in curing of elastomers are contemplated for usein the practice of the invention. One sulfur accelerator class that issuitable for use in the practice of this invention comprises metal saltsof disubstituted dithiocarbamates. The metal salts of disubstituteddithiocarbamic acid, which are suitable in the practice of thisinvention, may be represented by the structure: ##STR1## wherein X is anion derived from a metal selected from the group consisting of nickel,cobalt, iron, chromium, tin, zinc, copper, lead, bismuth, cadmium,selenium, and tellurium, n may vary from 1 to 6 and is equal to theformal valence of the metal, R1 and R2 are independently alkyl of 1 to 7carbon atoms.

Examples of the metal salts of disubstituted dithiocarbamic acid are:

bismuth dimethyldithiocarbamate

cadmium diamyldithiocarbamate

cadmium diethyldithiocarbamate

copper dimethyldithiocarbamate

lead diamyldithiocarbamate

lead dimethyldithiocarbamate

selenium dimethyldithiocarbamate

tellurium diethyldithiocarbamate

zinc diamyldithiocarbamate

zinc diethyldithiocarbamate

zinc dimethyldithiocarbamate

selenium dimethyldithiocarbamate

A second sulfur accelerator class that is also suitable for use in thepractice of this invention comprises the thiurams. Thiuram acceleratorsare prepared from secondary amines and carbon disulfide. They may berepresented by the following structure: ##STR2## wherein R₃ is an alkylgroup of 1 to 7 carbon atoms and n may have a positive value fromgreater than zero up to 6. Examples of thiuram type acceleratorsinclude:

tetrabutylthiuram disulfide

tetraethylthiuram disulfide

tetramethylthiuram disulfide

tetramethylthiuram monosulfide

These classes of sulfur accelerators as well as other suitable classesof sulfur accelerators such as the sulfenamides, thiazoles, thioureasand xanthates are described in further detail in The Vanderbilt RubberHandbook, pp 339-380. The sulfur accelerators described thereinencompass the classes of sulfur compounds which would be comprehended byone of skill in the art of curing elastomeric polymers as sulfuraccelerators. Simple mercaptans of the formula RSH are not included inthis class of sulfur accelerators.

Hydroquinones

The hydroquinones which are suitable in the practice of this inventionare described in detail in the Encyclopedia of Chemical Technology,Third Edition, vol. 19 pp 572-606. Examples of hydroquinonesparticularly useful in the practice of this invention are:

hydroquinone

hydroquinone di(beta-hydroxyethyl)ether

hydroquinone monomethyl ether

mono-tert-butyl hydroquinone

di-t-butyl hydroquinone

di-t-amyl hydroquinone

The sulfur accelerator and the hydroquinone are employed in amounts thatare sufficient to achieve the desired balance in cure characteristics.The weight ratio of hydroquinone compound to sulfur accelerator is from1:50 to 500:1 preferably from 1:25 to 250:1 more preferably from 1:25 to25:1, still more preferably from 1:10 to 10:1 and most preferably from1:1 to 5:1. The weight ratio of this blend to peroxide can range from0.5:100 to 1:2, preferably from 1:100 to 1:2, more preferably from 1:100to 1:4 and still more preferably from 1:25 to 1:20.

Coagents

Various vinyl and/or allyl monomers are used to enhance crosslinking andas such are often called crosslinking coagents. The effective coagentsare generally difunctional or polyfunctional vinyl and/or allylmonomers.

The use of these monomers or crosslinking coagents in the practice ofthis invention provides a number of advantages:

1) The extent of crosslinking as measured by M_(H), the maximum torqueshown by an oscillating disc rheometer is enhanced or maintained in thefinal cured polymer when scorch retarding compared with formulations notemploying coagents.

2) The solubility and ease of preparation of solutions of the peroxide,quinone and sulfur accelerator are surprisingly facilitated;

3) An important and unexpected enhanced phase and color stability isprovided in scorch retarding curing/crosslinking peroxide solutionformulations contemplated by the second composition of the invention.

4) It has surprisingly been found, for those compositions tested, wheningredients are combined in the proper order, the speed and ease ofdissolution and thus the preparation of the second composition aspectcompositions of the invention are made more rapid and easier. This orderis first coagent, second hydroquinone, third sulfur accelerator, lastperoxide or azo compound.

Blends of coagents may also be used in the practice of this inventionwherein monofunctional monomers may be used in combination with the di-or poly-vinyl and/or allyl monomers.

Representative monomers include but are not limited to the following:methyl methacrylate, lauryl methacrylate, allyl methacrylate,trimethylol propane triacrylate, triallyl cyanurate, triallylisocynaurate, triallyl phosphate, tetraallyloxyethane, allyldiglycol,carbonate, triallyltrimellitate, triallylcitrate, diallyl adipate,diallylterephthalate, diallyl oxalate, diallyl fumarate, ethylene glycoldimethacrylate, 2-hydroxyethyl methacrylate.

Other polyfunctional vinylic compounds such as liquid 1,2-polybutadienemay also be used.

Particular preferred monomers are selected from: allyl methacrylate,triallylcyanurate, triallyltrimellitate, triallylisocyanurate,allydiglycolcarbonate, diallyl oxalate, methyl methacrylate and blendsthereof.

The monomeric compounds, when incorporated into any of the compositionaspects of the invention, may be used in ratios of 100:1 to 1:100preferably 50:1 to 1:50, most preferably 10:1 to 1:10 with respect tothe combined amount of sulfur accelerators and quinones present.

Polymers

The thermoplastic and/or elastomeric polymers encompassed in the presentinvention may be defined as those natural or synthetic polymers whichare thermoplastic and/or elastomeric in nature, and which can becrosslinked (cured) through the action of a crosslinking agent. RubberWorld, "Elastomer Crosslinking with Diperoxyketals," October, 1983,pp.26-32, and Rubber and Plastic News, "Organic Peroxides for RubberCrosslinking," Sep. 29, 1980, pp. 46-50, describe the crosslinkingaction and crosslinkable polymers. Polyolefins suitable for use in thisinvention are described in Modern Plastics Encyclopedia 89 pp 63-67,74-75. Illustrative polymers include linear low density polyethylene,low density polyethylene high density polyethylene, chlorinatedpolyethylene, ethylene-propylene terpolymers, ethylene vinyl acetateethylene-propylene copolymers, silicone rubber, chlorosulfonatedpolyethylene, fluoroelastomers.

In addition, blends of two or more polymers may be employed. Thepolymers described above and the crosslinkable compositions preparedtherefrom may contain various other additives known to those skilled inthe art including fillers such as carbon black, titanium dioxide, andthe alkaline earth metal carbonates. Monomeric co-agents such astriallylcyanurate, allyldiglycolcarbonate, triallylisocyanurate,trimethylolpropane diallylether, trimethylolpropane trimethacrylate,various allylic compounds, methacrylates and acrylate compounds may alsobe added separately to the various polymers above. It is also well knownin the art that polymer containing compositions in general may alsocontain antioxidants, stabilizers, plasticizers, and processing oils.The crosslinkable compositions of this invention may also contain suchconventional additives.

The novel compositions can be incorporated into a masterbatch or carriercomprising various polyolefins and/or elastomers at levels from about 5to 80 percent by weight.

For ease of addition for certain processes, the scorch retardingcrosslinking composition, in the form of a homogenous liquid or meltablesolid, may be dispersed on an inert filler such as CaCO₃, silica or clayat levels from about 10 to 80 percent by weight.

The scorch retarding crosslinking composition can be incorporated into apolymeric thermoplastic and/or elastomeric material, as a preformedmixture or with the addition of each component separately, resulting inimproved scorch protection. The weight ratio of hydroquinone compound tosulfur accelerator in the first composition aspect of the invention maybe from 1:50 to 500:1, preferably from 1:25 to 250:1, more preferablyfrom 1:25 to 25:1, still more preferably from 1:10 to 10:1, and mostpreferably from 1:1 to 5:1. The weight ratio of the first compositionaspect to peroxide in the second composition aspect of the invention mayrange from 0.5:100 to 1:2, preferably from 1:100 to 1:2, more preferably1:100 to 1:4, and still more preferably 1:25 to 1:20. The peroxide,quinone, sulfur accelerator and optional coagent containing secondcomposition aspect of the invention may be incorporated into thepolymeric thermoplastic and/or elastomeric material in quantities toprovide a peroxide concentration in the crosslinkable compositionranging from 0.01 to 30 parts by weight, preferably from 0.01 to 20parts by weight, most preferably from 0.5 to 4.0 parts by weight foreach 100 parts by weight of polymer.

The crosslinkable composition may be heat cured to a time sufficient toobtain the desired degree of crosslinking. The heat curing has atemperature-time relationship which is primarily dependent on thepolymeric compound and the peroxide initiator present, but thatrelationship may be affected by other ingredients in the formulation. Itis customary to use a time equal to about 6 to 8 half-lives of theinitiator, but this may be varied based on experience at the option ofthe operator depending on the exact properties desired in the finalproduct. The inclusion of the scorch retarding compositions of thisinvention has no substantial effect on the time-temperature relationshipwhen compared to the relationship in a similar system without the scorchretarding composition.

Crosslinking (curing) may be carried out at a temperature of 100°-300°C. or more. The cure time is inversely related to the temperature.Systems employing the preferred initiators heat cure at temperature-timerelations of about 120°-200°C. and 0.5 to 30 minutes. The heat curingmay be carried out in any conventional fashion such as mold cures, oilbath cures (where oil does not harm the polymeric compound), oven cures,steam cures, or hot metal salt bath cures.

General Experimental Procedures

All formulations were compounded utilizing the C. W. BrabenderPlastigraph with type-5 mixing blades. Mixer temperatures are specifiedbelow for various resin types.

    ______________________________________    Resin Type            Temp (°C.)    ______________________________________    high density polyethylene (HDPE)                          140    low density polyethylene (LDPE)                          110    linear low density PE (LLDPE)                          125    ethylene-vinyl acetate (EVA)                          105 or less    ethylene-propylene-diene (EPDM)                          ambient temperature    monomers terpolymer    fluoroelastomer       ambient temperature    ______________________________________

To prepare crosslinkable compositions, except for the polymer, allcomponents of the composition, for example, the peroxide, adisubstituted dithiocarbamic acid, and hydroquinone were weighed at thedesired parts by weight resin into a ten dram vial and mixed to form ahomogeneous solution. The quantity of each ingredient expressed in partsper 100 parts of polymer is listed in each example.

For both thermoplastic and rubber (elastomeric) compositions, 100 partsby weight of polymer were fluxed in the mixer using a mixing speed of 30rpm at a mixing temperature designated in the specific examples. Thepreweighed component mixture in the vial was then slowly added to thefluxing resin. The composition was then allowed to mix for six (6)minutes, after which the composition was removed and subsequentlypressed into a flat plaque (of no specific thickness), using a Carverlaboratory press (Model C) set at the polymer melting point, folded andpressed at least six times to remove air bubbles and smooth out sample,and then the plaque was allowed to cool to room temperature.

Testing

Crosslinking evaluations were carried out on the prepared compositionsusing a Monsanto Oscillating Disk Rheometer (Model R-100).

The Monsanto Rheometer test procedure consists of an uncured sampleenclosed, under positive pressure, in a heated die cavity containing abiconical disk. The disk is oscillated (100 cycles/min) through an arcof 1° or 3° or 5°. The force, or torque, required to oscillate the diskis recorded as a function of time. This shear modulus is proportional tothe extent of crosslinking, and is a representation of the curereaction. The shear modulus increases as percent crosslinking increases.The test variables recorded from the rheometer were:

M_(H) --Maximum torque (in-lbs), a measure of crosslinking attained.

M_(L) --Minimum torque (in-lbs), a measure of viscosity of the compoundand an indicator of scorch. Increased M_(L) values are indicative ofscorch.

M_(H) -M_(L) --Difference between maximum and minimum torque values.This is useful in determining extent of crosslinking.

T_(C90) --Cure Time (minutes), time to reach 90% of maximum torque asdefined by (M_(H) -M_(L)) 0.9+M_(L).

T_(S2) --Scorch time (minutes), time required for torque to increase twoinch-pounds above M_(L)

T_(v) --Vulcanization time, calculated by T_(C90) -T_(S2), a measure ofcure rate, in which the curing rate is isolated from the scorch orprocessing phase.

ΔT_(S2) --Delta T_(S2) (minutes), the difference in scorch timecalculated by the T_(S2) of a scorch retarded peroxide containingpolymer formulation minus the T_(S2) for a comparable reference orcontrol peroxide containing polymer formulation. The cure is adjusted sothat (M_(H)) is virtually identical for both formulations.

Other reported "Delta" (Δ) values have been determined in similarfashion from the differences determined for the particular variable.

Torque values reported (M_(H) -M_(L)) are rounded off to the nearestwhole number. Scorch time values are rounded off to the nearest tenth ofa minute.

The following examples are provided to illustrate preferred embodimentsof the invention, and are not intended to restrict the scope thereof.

EXAMPLE 1

This example illustrates the desirable increase in scorch time change,delta T_(S2), when using a synergistic blend of a hydroquinone such ashydroquinone monomethyl ether (HQMME) and a dithiocarbamate such as zincdiamyldithiocarbamate (ZnDADTC) as a scorch retarding composition ascompared to the use of these additives separately in a dicumyl peroxidecure of a LLDPE (Union Carbide DFDA7530). Six scorch retardingcrosslinking compositions were evaluated (A-F)

    ______________________________________               A     B      C      D    E    F    Components   (Quantities in parts by weight)    ______________________________________    Dicumyl peroxide                 100     100    100  100  100  100    (100% assay)    HQMME        0       6.0    9.0  0    0    6.0    ZnDADTC (pure basis)                 0       0      0    3.0  9.0  3.0    ______________________________________

In order to accurately compare change in scorch time, delta T_(S2), foreach peroxide composition on the curing of LLDPE, the parts per hundredrubber (phr) use level of each blend (A-F) was adjusted to provide thesame magnitude of cure (M_(H)) for the LLDPE containing crosslinkablecompositions (G-L) below.

    ______________________________________    LLDPE COMPOSITIONS    parts of (A-F)              G      H       I     J     K     L    ______________________________________    M.sub.H = 60 in-lbs. for all samples (Monsanto ODR R-100 at    360° F., ±3° arc)    peroxide compo-              1.5A   1.94B   2.24C 1.72D 2.03E 2.19F    sitions per 100    parts of LLDPE    (by weight)    ______________________________________

The use levels of HQMME and/or ZnDADTC present in each composition areprovided below, along with the resulting changes in scorch time, deltaT_(S2), obtained at the equivalent degree of cure for the samples shownabove.

    ______________________________________           G     H       I       J     K     L    Components             (parts by weight)    ______________________________________    Dicumyl  1.5     1.83    2.05  1.62  1.72  1.95    peroxide    (100% assay)    HQMME    0       0.12    0.18  0     0     0.12    ZnDADTC  0       0       0     0.06  0.18  0.06    (pure basis)    LLDPE    100     100     100   100   100   100    T.sub.S2 (min)             5.9     8.0     9.3   6.1   8.5   10.1    .sub.Δ T.sub.S2 (min)             --      +2.1    +3.4  +0.2  +2.6  +4.2    Monsanto ODR at 290° F., ±3° arc    ______________________________________

The equal weight usage of HQMME and ZnDADTC singly in compositions H andJ provides a +2.1 and +0.2 improvement in scorch time respectively for atotal change in scorch time (ΔT_(S2)) of only +2.3 min. as compared to+4.2 min. improvement in scorch time for the synergistic combination incomposition L.

Using significantly higher concentrations of either additive, as incompositions I or K does not provide the scorch time improvementattained by the novel additive blend in composition L.

EXAMPLE 2

This example illustrates the desirable increase in scorch time change,delta T_(S2), when using a blend of a hydroquinone such asmono-t-butylhydroquinone (MTBHQ) and a thiuram such as tetrabutylthiuramdisulfide (TBTD) as compared to the singular use of these additives in adicumyl peroxide cure of EVA (U.S.I. EY901). Six peroxide compositionswere evaluated (A-F).

    ______________________________________            A    B       C       D     E     F    Components              (Quantities in parts by weight)    ______________________________________    Dicumyl Peroxide              100    100     100   100   100   100    (100% Assay)    MTBHQ     0      2.0     0     0     2.0   2.0    TBTD      0      0       2.0   4.0   2.0   4.0    ______________________________________

In order to accurately compare change in scorch time delta T_(S2) foreach peroxide composition on the curing of EVA, the phr use level ofeach blend (A-F) was adjusted to provide the same magnitude of cure(M_(H)) for the EVA compositions (G-L) below.

    ______________________________________             EVA COMPOSITIONS    parts of (A-F)               G       H       I     J     K    L    ______________________________________    peroxide   1.49A   1.60B   1.50C 1.55D 1.60E                                                1.70F    compositions per    100 parts of EVA    ______________________________________     M.sub.H = 45 in. lb. for all samples     Monsanto ODR at 360° F., ±3° arc

The use levels of MTBHQ and/or TBTD present in each composition areprovided below, along with the resulting change in scorch time, deltaT_(S2), obtained at equivalent degree of cure as indicated above.

    ______________________________________           G     H       I       J     K     L    Components             (parts by weight)    ______________________________________    Dicumyl  1.49    1.57    1.47  1.52  1.54  1.61    peroxide    (100% Assay)    MTBHQ    0       0.03    0     0     0.03  0.03    TBTD     0       0       0.03  0.06  0.03  0.06    EVA      100     100     100   100   100   100    T.sub.S2 (min)             4.4     6.0     7.0   8.4   9.4   10.8    .sub.Δ T.sub.S2 (min)             --      +1.6    +2.6  +4.0  +5.0  +6.4    ______________________________________     Monsanto ODR at 290° F., +3° arc

The equal weight usage of MTBHQ and TBTD singly in compositions H and Iprovide a +1.6 and +2.6 min. improvement in scorch time for a total of+4.2 min. as compared to +5.0 min. for the synergistic blend of thesetwo additives in composition K. The use of MTBHQ and TBTD singly incompositions H and J provide a corresponding +1.6 and +4.0 min.improvement in scorch time for a total of 5.6 min., as compared to 6.4min. for the synergistic blend of these two additives in composition L.

EXAMPLE 3

This example illustrates the desirable increase in scorch time change,delta T_(S2), when using a synergistic blend of a hydroquinone such asmono-t-butylhydroquinone (MTBHQ) and a thiuram such as tetrabutylthiuramdisulfide (TBTD) as compared to the singular use of these additives in a2,5-Dimethyl-2,5-di(t-butylperoxy) hexane cure of EVA (U.S.I EY901).Five peroxide compositions were evaluated (A-E).

    ______________________________________              A      B       C       D     E    Components  (Quantities in parts by weight)    ______________________________________    2,5-Dimethyl-2,5-di                100      100     100   100   100    (t-butylperoxy)hexane    MTBHQ       0        2.0     0     0     2.0    TBTD        0        0       2.0   4.0   2.0    ______________________________________

In order to accurately compare change in scorch time, delta T_(S2) foreach peroxide composition on the curing of EVA, the phr use level ofeach blend (A-E) was adjusted to provide the same magnitude of cure(M_(H)) for the EVA compositions (F-J) below.

    ______________________________________              EVA COMPOSITIONS    parts of (A-E)                F        G       H     I     J    ______________________________________    peroxide compositions                1.24A    1.30B   1.29C 1.36D 1.35E    per 100 parts of EVA    ______________________________________     M.sub.H = 50 in. -lb. for all samples     Monsanto ODR at 360° F., ±3° arc

The use levels of MTBHQ and/or TBTD present in each composition isprovided below, along with the resulting change in scorch time, deltaT_(S2), obtained at equivalent degree of cure as indicated above.

    ______________________________________              F      G       H       I     J    Components  (Quantities in parts by weight)    ______________________________________    2,5-Dimethyl-2,5-di                1.24     1.27    1.26  1.30  1.29    (t-butylperoxy)hexane    MTBHQ       0        0.03    0     0     0.03    TBTD        0        0       0.03  0.06  0.03    EVA         100      100     100   100   100    T.sub.S2 (min)                4.9      7.9     7.5   9.3   11.8    .sub.Δ T.sub.S2 (min)                --       +3.0    +2.6  +4.4  +6.9    ______________________________________     Monsanto ODR at 290° F., ±3° arc

The equal weight usage of MTBHQ and TBTD singly in compositions G and Hprovide a +3.0 and +2.6 min. improvement in scorch time for a total of+5.6 min. as compared to +6.9 min. for the synergistic blend of thesetwo additives in composition J.

EXAMPLE 4

This example illustrates the desirable increase in scorch time change,delta T_(S2), when using a synergistic blend of a hydroquinone such ashydroquinone monomethyl ether and a dithiocarbamate such as zincdiamyldithiocarbamate (ZnDADTC) as compared to the use of theseadditives singly in a1,1-bis-(t-butylperoxy)-3,3,5-trimethyl-cyclohexane cure of Nordel 1040EPDM.

In order to accurately compare change in scorch time, delta T_(S2), foreach composition on the curing of EPDM, the phr use level of theperoxide was adjusted to provide the same magnitude of cure (M_(H)) forthe EPDM compositions listed below. The additives included in thesystems were kept at constant levels.

    ______________________________________               EPDM COMPOSITIONS               A     B       C       D     E    Ingredient   (Quantity in parts by weight)    ______________________________________    Nordel 1040 (DuPont)                 100     100     100   100   100    N660 Black   25      25      25    25    25    1,1-bis-(t-butylperoxy)-                 2.2     2.7     2.3   2.5   2.7    3,3,5-trimethyl-cyclo-    hexane    HQMME        0       .063    0     0     .063    ZnDADTC (pure basis)                 0       0       .032  .095  .032    T.sub.C90 (min)                 9.5     9.5     9.5   9.5   9.5    M.sub.H (in-lb)                 63      63      63    63    63    Monsanto ODR at 300° F., ±3° arc    T.sub.S2 (min)                 6.3     9.6     6.4   7.7   11.3    .sub.Δ T.sub.S2 (min)                 --      +3.3    +0.1  +1.4  +5.0    Monsanto ODR at 250° F., ±3° arc    ______________________________________

The sum of the delta T_(S2) singular contributions from the HQMME andZnDADTC is +3.4 min (B and C). Unexpectedly, combination E added 5.0minutes of scorch time protection to the control (A). The same amount ofZnDADTC (D) added only 1.4 minutes. At levels such as (D) HQMME is notsoluble in the peroxide.

Therefore, E shows a synergistic effect with a significant increase inscorch time of 79% at 250° F. which can not be obtained by use of HQMMEor ZnDADTC used alone.

EXAMPLE 5

This example illustrates the increase in scorch time protection withhydroquinone-monomethyl ether (HQMME) and Zinc dibutyl dithiocarbamate(ZnDBDTC), which are solids, dissolved in a blend of peroxides, dicumylperoxide and 1,1-di (t-butylperoxy)-isopropyl!benzene (DTBPIPB) in thecuring of EVA (UE637).

    ______________________________________                A         B        C      D    Components  (Quantities in parts by weight)    ______________________________________    Dicumyl peroxide                60        60       60     60    1,1-di (t-butylperoxy)-    isopropyl!benzene                40        40       40     40    Zn DBDTC    0         2.5      0      2.5    HQMME       0         0        5.0    5.0    ______________________________________    EVA Compositions                E         F        G      H    Ingredients (Quantities in parts by weight)    ______________________________________    UE637       100       100      100    100    ZnO         4.0       4.0      4.0    4.0    antioxidant*                0.5       0.5      0.5    0.5    Component    A           2.0       .20      .25    .35    B           0         2.05     0      0    C           0         0        2.10   0    D           0         0        0      2.15    ______________________________________     *polymerized 1,2dihydro-2,2,4-trimethylquinoline (R. T. Vanderbilt)

Monsanto ODR results at 360° F., ±3° arc show all cures to be equal.M_(H) was 51 in.lb. and T_(C90) was 8.0 min.

Final use levels and change in scorch time are shown below. Monsanto ODRat 290° F., ±3° arc.

    ______________________________________                   E     F          G    H    Ingredient     (Quantity in parts by weight)    ______________________________________    dicumyl peroxide                   1.2   1.32       1.35 1.41    a,a-di (t-butylperoxy)-    isopropyl!benzene                   .8    .88        .90  .94    ZnDBDTC        0     .05        0    .05    HQMME          0     0          .10  .10    T.sub.S2 (min.)                   9.0   9.8        16.0 17.7    .sub.Δ T.sub.S2                   --    +.8        +7.0 +8.7    ______________________________________

ZnDBDTC and HQMME used individually improve T_(S2) by 0.8 min. and 7.0min. for a total of 7.8 min. The actual blend in composition (H) adds8.7 min. to the original scorch time with no retarder additive (E).

The usefulness of this system in a peroxide blend can be seen in thisTable with all samples cured the same, (51 in.lb.) and arrangedaccording to cure time, and half life.

    ______________________________________              Dicumyl              Peroxide                     Comp. E  Comp. H  DTBPIPB    ______________________________________    T.sub.C90 @ 360° F. (min.)                6.2      8.0      8.0    10.2    T.sub.S2 @ 290° F. (min.)                7.1      9.0      17.7   13.2    ______________________________________

A common practice to increase scorch time is to blend or totallysubstitute a peroxide with a higher half life, for example the use ofDTBPIPB to replace dicumyl peroxide. A disadvantage to this practice isthat a significant improvement in scorch time is obtained at the expenseof decreased productivity, e.g. longer cure times. A blend of these twoperoxides (composition E) provides intermediate cure and scorch times.In the practice of this invention (composition H) one unexpectedlyobtains a significantly longer scorch time not obtainable with thehigher half life initiator DTBPIPB when used alone, without thedisadvantage of a longer cure time.

EXAMPLE 6

This example illustrates that the hydroquinone compound and sulfuraccelerator may be incorporated into a masterbatch to be added to thepolymer to be crosslinked, separate from the peroxide. An EVA (UE634U.S.I.) was used as the carrier for the scorch retarders which are usedwith and without a monomeric cocuring agent. Free flowing pellets arethe final form.

    ______________________________________                  Masterbatch components                  A      B                  (Quantities in                  parts by weight)    ______________________________________    EVA             100      100    HQMME           4        2    ZnDADTC (50%)   4        2    TAIC*           0        6    ______________________________________     *triallylisocyanurate

Dicumyl peroxide, with these masterbatches, was used to crosslink thesame EVA used at equal weights to peroxide solutions containing scorchretarders used to prepare compositions (D) and (F). Thus the final EVAformulations (E) and (G) prepared using the above (A), and (B)masterbatches are equivalent in composition to (D) and (F) respectively.

    ______________________________________    C           D       E       F     G     H    (Quantities in parts by weight)    ______________________________________    EVA     100     100     97.5  100   95.0  100    Batch A 0       0       2.7   0     0     0    Batch B 0       0       0     0     5.5   0    HQMME   0       .1      0     .1    0     .1    ZnDADTC 0       .1      0     .1    0     .1    TAIC    0       0       0     .3    0     0    Dicumyl 2.0     2.0     2.0   2.0   2.0   2.3    peroxide    Monsanto ODR at 360° F., ±3° F.    M.sub.H (in. lb.)            68.1    60.0    60.8  69.2  68.6  66.0    T.sub.C90 min.            5.1     5.3     5.3   4.9   4.9   5.2    Monsanto ODR at 290° F.    T.sub.S2 min.            3.6     10.0    9.7   9.5   9.2   8.9    ______________________________________

The masterbatch procedure has more chances for weight loss and is theonly reason for the slight difference in results between (D) and (E).TAIC is well known for increasing the state of the cure while havinglittle effect on cure and scorch times. On a weight basis, its use isslightly better than additional dicumyl peroxide in this formulation,(F) and (G) vs. (H) as it restores the M_(H) with only a small amountcompared to normal use levels and has little effect on T_(S2).Masterbatch (B), thus, allows variation of scorch retarder level withoutchanging peroxide level or affecting M_(H). When using the masterbatchapproach, there are also no solubility or long term homogeneity concernsfor the peroxide used.

EXAMPLE 7

These examples show that the composition may be added dispersed on afiller for use in the rubber industry where powders or solids arepreferred. Di-t-amyl hydroquinone (DTAHQ) and a sulfur accelerator blendfrom U.S. Pat. No. 4,632,950 shows a synergistic effect in scorch timeswhen combined along with advantages in cure in Nordel 1040 EPDM curedwith 1,1-bis(t-butylperoxy)-3,3,5-trimethyl cyclohexane, 40% on afiller.

    ______________________________________            A    B       C       B & C D     E    Composition              (Quantities in parts by weight)    ______________________________________    Nordel 1040              100    100     100   --    100   100    N550 black              60     60      60    --    60    60    Sunpar 2280 oil              10     10      10    --    10    10    1,1-bis-(t-    butylperoxy)-    3,3,5-tri-    methylcyclo-    hexane (40%)              6.0    6.0     6.0   --    6.0   6.0    di-t-amyl 0      .45     0     --    .45   .516    hydroquinone    Zinc dimethyl-              0      0       .06   --    .06   0    dithio carbamate    Copper dimethyl-              0      0       .006  --    .006  0    dithiocarbamate    Monsanto ODR at 300° F. at ±3° arc    M.sub.H (in lbs.)              48     51      44    --    50    51    T.sub.C90 (min.)              7.4    7.5     7.1   --    6.6   8.2    T.sub.V (min.)              6.1    6.0     5.7   --    4.9   6.5    Monsanto ODR at 250° F.    T.sub.S2 (min.)              6.6    9.1     7.1   ,--   11.6  9.9    .sub.Δ M.sub.H              --     +3      -4    -1    +2    +3    .sub.Δ T.sub.C90              --     +.1     -.3   -.2   -.8   +.8    .sub.Δ T.sub.V              --     -.1     -.4   -.5   -1.2  +.4    .sub.Δ T.sub.S2              --     +2.5    +.5   +3.0  +5.0  +3.3    ______________________________________

B and C are prior art scorch inhibitor systems which if combinedadditively as in column (B & C) would increase T_(S2) at 250° by 3.0min. with slight changes to the state and rate of cure. The sulfuraccelerators lower the state of cure and di-t-amyl hydroquinone at lowlevels acts as a coagent in this polymer and peroxide as a benzoquinonederivative works in EPM. The actual composition (D) increases T_(S2)over (A) by 5.0 min. at higher M_(H) at a 20% faster vulcanization time.Simply adding more DTAHQ causes a slightly longer T_(S2) but T_(v) i.e.,vulcanization time, in (E) is one-third longer than (D).

EXAMPLE 8

This example also illustrates the advantage of a hydroquinone and sulfuraccelerator blend when added with a filler extended peroxide for anelastomer cure. 2,5-dimethyl-2,5-di(t-butylperoxy)hexane 45% on a CaCO₃and silica filler, when blended with a small amount of di-t-amylhydroquinone and tetramethylthiuram monosulfide results in better scorchtime and cure time than these compounds used alone at equal weight incuring a fluoroelastomer.

    ______________________________________                  A    B        C      D    Composition     (Quantities in parts by weight)    ______________________________________    FC2480*         100    100      100  100    N774 black      20     20       20   20    Ca(OH).sub.2    3.0    3.0      3.0  3.0    TAIC            2.5    2.5      2.5  2.5    2,5-dimethyl-2,5-                    2.5    2.5      2.5  2.5    di(t-butylperoxy)-    hexane (45%)    di-t-amyl hydroquinone                    0      .05      .10  .05    tetramethylthiuram                    0      0        0    .05    monosulfide    Monsanto ODR at 350° F. ±3° arc    M.sub.H (in-lb.)                    96     99       99   98    T.sub.C90 (min.)                    7.6    8.4      9.4  7.7    Monsanto ODR at 300° F.    T.sub.S2 (min.) 4.9    7.0      8.7  10.8    ______________________________________     *FC2480 = fluoroelastomer from 3M

The first two additions of 0.05 parts of the hydroquinone increasescorch time by only 2 minutes each and cure time by one minute each.Sulfur accelerators or accelerator blends will increase T_(S2) at 300°by only 0.8 to 1.6 minutes at this level without changing the cure time.Higher sulfur levels would not be preferred because of odor and anegative effect on aging. In sample D, adding tetramethyl thiurammonosulfide instead of additional di-t-amyl hydroquinone, scorch time isimproved by 5.9 minutes over the control A, instead of the 3.8 minutesimprovement in C, while the cure time (T_(C90)) is reduced back to thedesirable original value. This balance is not possible with eithercompound used individually.

Changing to a higher temperature half life peroxide such as2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3 to increase scorch safety (aswell as cure time) results in a T_(S2) at 300° F. of 9.8 min., or animprovement of 4.9 minutes at a lower state of cure.

EXAMPLE 9

This example shows storage stability of scorch retarded peroxidesolutions. Various formulations and a control were aged three times atthree different temperatures slightly over normal storage temperaturesand assayed for percent peroxide.

    __________________________________________________________________________                   A     B     C     D    Components     (parts by weight)    __________________________________________________________________________    dicumyl peroxide                   100   96.0  96.0  88.0    mono-t-butyl hydroquinone                   0     2.0   2.0   0    hydroquinone monomethyl ether                   0     0     0     6.0    Zn diamyl dithiocarbamate (50%)                   0     2.0   0     6.0    tetrabutyl thiuram disulfide                   0     0     2.0   0    Peroxide assay after aging conditions (%)                      40° C.    Temperature           30° C.                      (time in weeks)                                50° C.    Start  2   4  8   2  4   8  2   4  8    __________________________________________________________________________    Peroxide    formulation    A   92.0           90.9               92.2                  92.0                      89.3                         92.2                             91.8                                92.0                                    91.7                                       92.7    B   88.6           89.8               90.0                  87.4                      88.0                         88.3                             87.2                                87.3                                    87.7                                       86.5    C   87.3           86.7               85.9                  86.7                      85.7                         86.3                             86.2                                86.3                                    87.6                                       87.2    D   87.8*           86.5               87.6                  89.3                      86.3                         87.2                             89.3                                86.4                                    87.1                                       88.7    __________________________________________________________________________     *Sample D was made with a higher assay dicumyl peroxide so the final     unaged assay was similar to B and C.

Peroxide assays (±2%) show no pattern of degradation, therefore they arestable at normal storage temperatures.

EXAMPLE 10

Solubility of some additives varies in different classes of peroxidesand also over time. This can be improved by adding a liquid or solidco-curing agent. The normal application of such co-curing agent(coagent) in improving the state of cure is useful here, but such agentsappear to unexpectedly improve solubility and more importantly stabilityof additives, sometimes lowering melting point, and to increase ease ofpreparation of the peroxide solution without adding inert extenders. Thetable in this example shows two peroxide solutions with a small portionof the peroxide replaced with a coagent and a comparison of visualchanges over time.

    ______________________________________    Formulation   A        B        C      D    Ingredient    (parts by weight)    ______________________________________    dicumyl peroxide                  50       50       0      0    n-butyl-4,4-bis(t-butyl-                  50       25       0      0    peroxy)valerate    2,5-dimethyl-2,5-di(t-                  0        0        100    85    butylperoxy)hexyne-3    hydroquinone monomethyl                  4.0      4.0      5.0    5.0    ether    Zn diamyl dithiocarbamate                  2.0      2.0      0      0    (50%)    tetramethyl thiuram mono-                  0        0        0.5    0.5    sulfide    triallyl trimellitate                  0        25       0      0    triallyl cyanurate                  0        0        0      15    Age-Time      (2 months)    (1 month)    Color         brown    none     slight slight    Insolubles    yes      none     slight none    ______________________________________

Solutions A and B were originally clear and C and D were clear andslightly yellow but A and C showed a change in solubility of additives.The coagents suprisingly facilitated the rate and amount of solubilityof the scorch retarders with an active ingredient and more importantlyunexpectedly stabilized mixtures such as B and D.

EXAMPLE 11

This example shows the activity of solutions from the last example in acrosslinking reaction. The solutions were compared to a single peroxidecontrol in crosslinking the same polymer before and after aging. Mixingand curing conditions in the Monsanto Rheometer were held constant atall times.

    ______________________________________    Formulation   A       B        C      D    Ingredient    (parts by weight)    ______________________________________    dicumyl peroxide                  53      100      0      0    n-butyl-4,4-bis(t-butyl-                  25      0        0      0    peroxy)valerate    2,5-dimethyl-2,5-di(t-                  0       0        85     100    butylperoxy)hexyne-3    hydroquinone monomethyl                  0       0        5.0    0    ether    di-t-amyl hydroquinone                  2.0     0        0      0    Zn diamyl dithiocarbamate                  1.0     0        0      0    (50%)    tetramethyl thiuram mono-                  0       0        0.5    0    sulfide    triallyl cyanurate                  22      0        15     0    Original cure properties crosslinking EVA (±3° arc)    Solution in EVA (phr)                  1.50    1.50     2.11   2.00    Rheometer temperature                  360° F.   380° F.    M.sub.H in. lb.                  51.1    51.2     71.6   71.8    T.sub.C90 min.                  4.7     5.3      7.7    8.1    Rheometer temperature                  290° F.   320° F.    T.sub.S2 min. 8.4     7.3      9.9    2.7    A and C aged 1 month at 32° C., cure properties in same EVA    Rheometer temperature                  360° F.   380° F.    M.sub.H in. lb.                  51.4    51.4     72.7   71.8    T.sub.C90 min.                  4.5     5.2      7.9    7.7    Rheometer temperature                  290° F.   320° F.    T.sub.S2 min. 8.5     7.3      10.2   2.8    ______________________________________

There is no change in crosslinking efficiency as measured by M_(H) andno loss of scorch retardation which is measured by T_(S2) after ageingone month at an average temperature of 32° C. The solutions retainsolubility and efficiency with the TAC coagent without dilution withinert ingredients. Unexpectedly we found that the order of addition ofthe various additives and peroxide can greatly affect the speed and easeof preparing a homogenous solution. A formulation such as C, in thisexample, is prepared more quickly by adding peroxide last. HQMME(melting point of 54° C.) and TMTM (105° C.) are very soluble in TAC(27° C.) resulting in a mixture which melts at about 15° C. and thenblends quickly with DMDBPH-3. Mixing in the order of formulation (C) aslisted could take up to ten times longer. Samples A and B have equalcrosslinking efficiency at equal weight. Slightly more of solution C isused to equal D although extra peroxide or co-agent alone could be usedas relative efficiency varies with the polymer used. Varying the levelof C has the least effect on scorch time.

EXAMPLE 12 Crosslinking High Density Polyethylene (HDPE)

Resin: High density polyethylene having melt flow index (MFI) 38 g/10min. at 190° C. and Sp. Gr. 0.941-0.98 g/cc

This Example illustrates the improvement in scorch time with minimaleffect on cure time obtainable when crosslinking HDPE with a typicalscorch retarding crosslinking composition of the invention.

    ______________________________________    Peroxide Solutions:                A       B       C     D     E    Ingredients (Quantities in parts by weight)    ______________________________________    2,5-dimethyl-                0.75    0.75    0.75  0.75  0.75    2,5-di(t-butylperoxy)    hexyne-3    Triallylcyanurate                0.15    0.15    0.15  0.15  0.15    Hydroquinone    Monomethyl ether                --      0.08    --    0.08  0.08    Tetramethyl Thiuram    Monosulfide --      --      0.01  0.01  0.02    ______________________________________    Solutions Mixed Into HDPE Resin    Batch                F       G       H     I     J                (Quantities by weight)    ______________________________________    Resin       100     100     100   100   100    Solution A  9.5     --      --    --    --    Solution B  --      0.8     --    --    --    Solution C  --      --      0.5   --    --    Solution D  --      --      --    0.8   --    Solution E  --      --      --    --    0.8    ______________________________________              Monsanto ODR R-100 Cures at ±3° arc.              F     G       H       I     J    ______________________________________    M.sub.H (in-lbs) at 400° F.                30.4    29.8    30.4  32.2  33.2    T.sub.C90 (min.) at 400° F.                6.8     7.0     6.1   7.0   7.0    T.sub.S2 (min.) at 350° F.                9.1     10.5    8.5   12.1  12.4    .sub.Δ T.sub.S2 (min.) at 350° F.                --      +1.4    -0.6  +3.0  +3.3    ______________________________________

A solution of 2,5-dimethyl 2,5-di(t-butyl peroxy) hexyne-3 withtriallylcyanurate (TAC) and hydroquinone monomethyl ether (HQMME)represented by formulation "G" provides a slight improvement in scorchtime as compared to the control (formulation "F"). Using a small amountof tetramethylthiuram monosulfide, formulation "H", actually results inan adverse effect on scorch time (a decrease in T_(S2) versus thecontrol). Quite unexpectedly, a blend of these additives "I" results ina significant improvement in scorch time which cannot be attained by theadditive effect of the materials used separately. Using more quinone toenhance scorch protection will continue to adversely reduce the finalcure (M_(H)). The unique composition of this invention "I" also providesan unexpected increased level of HDPE crosslinking as compared to "G"and even the control "F". To further support this unexpected synergism,increasing the amount of thiuram in formulation "J" shows continuedimprovement in crosslinking and scorch time protection.

EXAMPLE 13

This example describes the synergistic increase in scorch timeprotection that can be obtained when a sulfur accelerator of thethiazole sulfenamide class is used in combination with a hydroquinonetype compound. Thus an EVA containing two antioxidants is crosslinkedwith a scorch retarding crosslinking composition consisting of ahomogeneous solution of dicumyl peroxide, N-cyclohexyl-2-benzothiazolesulfenamide and hydroquinone monomethyl ether.

The two antioxidants used were supplied by R. T. Vanderbilt and arelisted below.

Agerite MA: polymerized trimethyl dihydroquinoline

Vanox ZMTI: Zn 2-mercaptotoluimidazole

In the compositions listed below, the level of peroxide (dicumylperoxide) was adjusted in order to provide equivalent state of cure asmeasured by the Monsanto ODR.

    ______________________________________    FINAL POLYMER COMPOSITION:                      A      B       C     D    ______________________________________    EVA UE637 (USI)   100    100     100   100    Agerite MA        0.5    0.5     0.5   0.5    Vanox ZMTI        0.5    0.5     0.5   0.5    dicumyl peroxide  2.00   2.14    2.12  2.12    N-cyclohexyl-2-   0      0.04    0     0.04    benzothiazole    sulfenamide    hydroquinone      0      0       0.06  0.06    monomethyl ether    MONSANTO ODR CURE AT 360°, 3° arc    M.sup.H (in-lbs)  34     34      34    33    TC90 (min)        6.4    6.2     6.3   6.4    MONSANTO ODR SCORCH EVALUATION AT 290° F., 3° arc    TS.sub.2 (min)    7.9    10.1    13.2  16.0    DELTA T.sub.S2 (min)                      --     2.2     5.3   8.1    ______________________________________

Using the scorch retarder additives N-cyclohexyl-2-benzothiazolesulfenamide, in system "B" and the hydroquinone monomethyl ether, insystem "C" separately provided a corresponding improvement in scorchprotection of 2.2 and 5.3 respectively, versus the control "A". Usingboth of these in combination, one would expect an improvement of about2.2+5.3=7.5 minutes. However as contemplated by this invention, thesynergistic combination of these additives in system "D" provides asignificantly higher improved scorch protection of 8.1 minutes, with nosignificant loss in the degree of crosslinking or cure rate performance.

ADDITIONAL FREE RADICAL INITIATORS

An addition preferred class of dialkyl peroxides included among the freeradical initiators contemplated by the invention are those having theFormula: ##STR3## wherein R⁴ and R⁵ may independently be in the meta orpara positions and may be the same or different and are selected fromhydrogen, or straight or branched chain lower alkyl of from 1 to aboutsix carbon atoms.

We claim:
 1. An improved composition for inclusion during and forretarding scorch during the compounding of thermoplastic polymers,curable with organic peroxides, elastomeric polymers, curable withorganic peroxides, and mixtures of thermoplastic and elastomericpolymers, curable with organic peroxides, in the presence of freeradical curing agents selected from the group organic peroxides toproduce compounded polymers and for subsequent free radical cure of saidcompounded polymers by decomposition of the free radical curing agent insaid compounded polymer which improved composition is prepared by mixingas the essential ingredients:a) sulfur accelerator selected from thegroup dithiocarbamates, thiurams, thiazoles, sulfenamides, thioureas,and xanthates; b) hydroquinone in a weight ratio of 1:50 to 500:1 tosulfur accelerator; c) free radical initiator selected from the groupconsisting of organic peroxides in a weight ratio of 2:1 to 100:0.5 tothe total amount of sulfur accelerator and hydroquinone; and d) coagentselected from the group consisting of polyfunctional vinyl monomers,polyfunctional allyl monomers, mixtures of monofunctional vinyl monomerswith polyfunctional vinyl monomers, mixtures of monofunctional vinylmonomers with polyfunctional allyl monomers, mixtures of monofunctionalallyl monomers with polyfunctional vinyl monomers and mixtures ofmonofunctional allyl monomers with polyfunctional allyl monomers in aweight ratio of 100:1 to 1:100 by weight based on total weight ofhydroquinone and sulfur accelerator.
 2. A composition as defined inclaim 1 wherein the organic peroxide is selected from the groupconsisting of dialkyl peroxides, diperoxyketals and mixtures thereof. 3.A composition as defined in claim 2 wherein the dialkyl peroxides areselected from dicumylperoxide; alpha, alpha-bis (t-butyl peroxy)diisopropylbenzene; t-butyl cumyl peroxide;2,5-dimethyl-2,5-di(t-butylperoxy)-hexane;2,5-dimethyl-2,5-di(t-butylperoxy)-hexyne-3;2,5-dimethyl-2,5-di(t-amylperoxy)-hexyne-3; di-t-amylperoxide; 1,3,5-tri(t-butylperoxy)-isopropyl!-benzene;1,3-dimethyl-3-(t-butylperoxy)butanol; and mixtures thereof.
 4. Acomposition as defined in claim 2 wherein the diperoxyketal initiatorsare selected from the group consisting of: 1,1-di(t-butylperoxy)cyclohexane; n-butyl-4,4-di(t-amylperoxy) valerate;ethyl-3,3-di(t-butylperoxy)-butyrate; 2,2-di(t-amylperoxy)-propane;3,6,6,9,9-pentamethyl-3-ethoxy carbonylmethyl-1,2,4,5-tetraoxacyclonane;n-butyl-4,4-bis(t-butylperoxy)-valerate;ethyl-3,3-di(t-amylperoxy)-butyrate and mixtures thereof.
 5. Acomposition as defined in claim 1 wherein the sulfur accelerator isselected from compounds represented by the structure: ##STR4## wherein Xis an ion derived from a metal selected from the group consisting ofnickel, cobalt, iron, chromium, tin, zinc, copper, lead, bismuth,cadmium, selenium and tellurium, n may vary from 1 to 6 and is equal tothe formal valence of the metal ion, and R₁ and R₂ are independentlyalkyl of 1 to 7 carbon atoms.
 6. A composition as defined in claim 1wherein the sulfur accelerator is selected from compounds represented bythe formula ##STR5## wherein R₃ is an alkyl group of 1 to 7 carbon atomsand n may have a positive value from greater than zero up to about
 6. 7.A composition as defined in claim 1 wherein the hydroquinone ishydroquinone monomethyl ether, the sulfur accelerator is zincdiamyldithiocarbamate, and the free radical initiator is dicumylperoxide.
 8. A composition as defined in claim 1 wherein thehydroquinone is mono-t-butylhydroquinone, the sulfur accelerator istetrabutylthiuram disulfide and the free radical initiator is dicumylperoxide.
 9. A composition as defined in claim 1 wherein thehydroquinone is mono-t-butylhydroquinone, the sulfur accelerator istetrabutylthiuram disulfide and the free radical initiator is2,5-dimethyl-2,5-di(t-butylperoxy) hexane.
 10. A composition as definedin claim 1 wherein the hydroquinone is hydroquinone monomethyl ether,the sulfur accelerator is zinc diamyldithiocarbamate, the free radicalinitiator is 1,1-bis-(t-butylperoxy)-3,3,5-trimethyl-cyclohexane.
 11. Acomposition as defined in claim 1 wherein the hydroquinone ishydroquinone monomethyl ether, the sulfur accelerator is zincdibutyldithiocarbamate and the free radical initiator is a mixture ofdicumyl peroxide and 1,1-di (t-butylperoxy) isopropyl!-benzene.
 12. Acomposition as defined in claim 1 wherein the coagent istriallylcyanurate.
 13. A composition as defined in claim 1 wherein thecoagent is triallyltrimellitate.
 14. A composition as defined in claim13 wherein the hydroquinone is hydroquinone monomethylether, the sulfuraccelerator is zinc diamyldithio carbamate and the free radicalinitiator is a mixture of dicumylperoxide andn-butyl-4,4-bis(t-butylperoxy) valerate.
 15. A composition as defined inclaim 12 wherein the hydroquinone is mono-t-butyl hydroquinone, thesulfur accelerator is zinc diamyldithio carbamate, and the free radicalinitiator is a mixture of dicumyl peroxide andethyl-3,3-di-(t-butylperoxy) butyrate.
 16. A composition as defined inclaim 12 wherein the hydroquinone is hydroquinone monomethyl ether, thesulfur accelerator is tetramethylthiuram monosulfide and the freeradical initiator is 2,5 dimethyl-2,5-di(t-butylperoxy)-hexyne-3.
 17. Acomposition as defined in claim 12 wherein the hydroquinone ishydroquinone monomethyl ether, the sulfur accelerator istetrabutylthiuram disulfide and the free radical initiator is a mixtureof dicumyl peroxide and ethyl 3,3-di-(t-butylperoxy)butyrate.
 18. Acomposition as defined in claim 12 wherein the hydroquinone ishydroquinone monomethyl ether, the sulfur accelerator istetrabutyl-thiuram disulfide and the free radical initiator is dicumylperoxide.
 19. A composition as defined in claim 1 wherein the essentialingredients are mixed substantially contemporaneously.
 20. A compositionas defined in claim 1 wherein any three of the essential ingredients aremixed substantially contemporaneously to prepare a first submixture andthe fourth essential ingredient is then added to the first submixture.21. A composition as defined in claim 1 wherein any two of the essentialingredients are combined to form a first submixture; the remaining twoessential ingredients are combined to form a second submixture; and thefirst and second submixtures are then combined.
 22. A composition asdefined in claim 1 wherein any two of the essential ingredients arecombined to form a first submixture; one of the remaining essentialingredients is combined with the first submixture to prepare a secondsubmixture; and the remaining uncombined essential ingredient iscombined with the second submixture.